Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation System (PCV):

The PCV valve is operated by the intake manifold vacuum. When the engine is running at idle, the PCV valve is opened slightly and a small amount of blow-by gas is drawn into the engine.
At higher engine speeds, the PCV valve is further opened and a larger amount of blow-by gas is drawn into the engine.
The PCV system consists of the PCV valve and assorted vacuum lines. The PCV valve controls the amount of blow-by gases that are pulled into the engine.